This invention relates to a shock wave generator, particularly for the fragmentation of concrements in hollow biological organs having a light-transmitting, particularly laser-light-transmitting light guide and a converter arranged at the distal light guide end which is equipped with a shock wave outlet zone and an ionization surface which, when a light pulse impinges on it, initiates a shock wave in the surrounding fluid.
Known shockwave generators of this type (e.g. DE-OS 37 36 953) are used as flexible application systems in intracorporal lithotripsy for producing laser-induced shock waves by means of the optical breakdown effect. These known shock wave generators have extremely small light guide and converter diameters of a magnitude of 1 to 2 mm. The converter is constructed as a hollow-cylindrical receiving housing which coaxially reaches around the light guide at the distal light guide end, and is open at one side. For reducing the light pulse density required for triggering the breakdown effect, the converter is equipped with a metallic ionization web which penetrates the shock wave emerging lumen of the converter in the area of the open housing end. The ionization surface of this ionization web faces the distal light guide end and extends vertically with respect to the beaming axis of the impinging light pulses, with a shock wave being generated in the surrounding fluid.
This shock wave, at least partially, first travels in the direct beaming area of the ionization surface inside the converter housing back to the light guide and to the interior housing walls, where it is reflected, before it can leave the converter by way of the outlet zone narrowed down by the ionization web and travel in the direction of the concrement to be fragmented. As a result of the energy loss of the shock wave on the way between the ionization surface and the converter outlet, shock wave generators of this type have a limited efficiency and durability, mainly in the area of the distal light guide end situated in the main direction of the backwards-travelling shock wave.
It is an object of the invention to construct an optoacoustic shock wave generator of the initially mentioned type in such a manner that, by means of an improved guiding of the shock wave in the converter, the usable electric-wave energy and the stability of the shock wave generator are clearly increased.
According to the invention, this object is achieved by means of the shock wave generator constructed such that the ionization surface extends obliquely sloped with respect to the beaming axis of the impinging light pulse, and the shock wave outlet zone of the converter is arranged in the direct shock wave beaming area of the ionization surface.
In the case of the shock wave generator according to the invention, it is ensured, as a result of the special assignment of the ionization surface with respect to the beaming axis of the light guide, on the one hand, and of the shock wave outlet zone, on the other hand, that the shock wave load of the generator, mainly in the light-guide-side converter areas which are particularly sensitive in this respect, is reduced considerably and the shock wave propagates largely unhindered from the ionization surface, by way of the converter outlet, to the application point. As a result, the shock wave energy which can be used at the application point is increased considerably in relation to the beamed-in light pulse energy, and the mechanical stability of the shock wave generator is clearly improved. The shock wave generator according to the invention is therefore excellently suitable for the direct fragmentation of concrements by shock waves at points which are difficult to reach, such as urinary or renal calculi in the human body.
In a further advantageous development of the invention, the ionization surface is preferably sloped at an angle of 20.degree. to 60.degree. with respect to the beaming axis of the light pulse, whereby, without any focussing of the light pulse, a sufficiently high luminance can be achieved at the ionization surface with a simultaneous particularly advantageous mutual assignment of the distal light guide end, the ionization surface and the outlet zone of the converter. So that the renewal of the ionization surface, at which the luminance of the light pulses required for initiating the breakdown effect must be in the magnitude of 10.sup.9 W/cm.sup.2, takes place without any problems, the ionization surface is preferably constructed at an exchangeable carrier element of the converter.
In order to effectively prevent in a simple manner a penetrating of floating particles, such as fragments of the concrement to be broken up, into the beaming path of the light pulses between the distal guide end and the ionization surface, a rinsing duct is expediently provided which in addition to the light guide, is connected to the converter and is used for supplying a rinsing fluid which flows around the distal light guide end and flows off toward the ionization surface; and in view of a particularly advantageous rinsing of the interior of the converter, the rinsing duct, preferably contains several rinsing-fluid outlet openings which are uniformly distributed in circumferential direction in the area of the distal guide end, in which case, a water-containing fluid is expediently used as the rinsing fluid which exhibits the desired optical characteristics concerning a low-threshold triggering of the breakdown effect as well as permits a transmission of the shock wave aimed directly at the application point which is as low in losses as possible.
For manufacturing reasons, the ionization surface is preferably constructed to be flat; however, it may optionally, for example, in view of a uniform luminance distribution, in the case of a generally slightly divergent inherent beaming characteristic of the light guide, also be bent.
According to a particularly preferred aspect of the invention, the converter consists of a hollow-cylindrical receiving housing which contains a carrier element which, in the manner of a finger, projects beyond the open housing end and is provided with the ionization surface, in which case, an outlet zone is obtained laterally of the housing axis which is no longer restricted by the inside diameter of the housing and through which the shock wave created at the ionization surface can pass almost completely on its direct path in the direction toward the application point. In this case, the beaming axis of the light guide in view of a simple fastening of the light guide, expediently extends in the direction of the central axis of the housing, in which case, the light guide can not only be fastened coaxially preferably--eccentrically with respect to the central axis of the housing in the receiving housing, in which case, the eccentric fastening results in a flatter slope of the ionization surface with respect to the central axis of the housing and therefore in an enlargement of the outlet zone and a more forwardly directed shock wave propagation. For an arrangement of the ionization surface which is directed further away from the open housing end toward the front, it is recommended to fasten the light guide obliquely with respect to the central axis of the housing in the receiving housing.
According to another variant of the invention which is particularly simple with respect to manufacturing, in connection with a converter which is again constructed as a hollow-cylindrical receiving housing, a circumferential beaming characteristic at the distal light guide end which is achieved by an oblique, proximal-side coupling-in of the light pulse is utilized in such a manner that the light pulse, as an annular cone which is coaxial with respect to the central axis of the housing, is aimed obliquely at the part of the interior wall of the cylinder which is adjacent to the open housing end and which forms the ionization surface. By means of the distribution of the light pulse which is uniform in circumferential direction and extends over the annular zone extending around the housing opening, the stability of the converter is further increased and it is ensured at the same time that the forming shock wave can propagate on a direct path by way of the free housing opening unhindered toward the front to the application point, thus, for example, to the calculus to be destroyed.
The invention will now be explained in detail by means of embodiments shown in the figures.
In a very schematical enlarged representation,